<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Viewport</title>
  <style>
    body {
      margin: 0;
    }
    .wrap {
      width: 750px;
      margin: auto;
      box-sizing: border-box;
      display: grid;
      grid-template-columns: 1fr 1fr;
      grid-template-rows: 667px;
      color: #fff;
      font-size: 18px;
    }
    .item {
      background: cornflowerblue;
    }
    .item:last-child {
      background: darkgreen;
    }
  </style>
</head>
<body>
  <div class="wrap">
    <div class="item">50%</div>
    <div class="item">50%</div>
  </div>
</body>
</html>